The present application relates to an electrode that includes a carbon material, and to a secondary battery that uses the electrode.
Various electronic apparatuses such as a mobile phone and a mobile information terminal device (PDA) have been widely used, and it has been demanded to further reduce the size and the weight of the electronic apparatuses and to achieve their longer lives. Accordingly, as an electric power source, a battery, in particular, a compact and light-weight secondary battery having high energy density has been developed.
In these days, application of the secondary battery is not limited to the above-described electronic apparatuses, and various other applications thereof have been considered. Examples of such various applications may include a battery pack attachably and detachably mounted on the electronic apparatus or the like, an electric vehicle such as an electric automobile, an electric power storage system such as a home electric power server, and an electric power tool such as an electric drill.
There have been proposed secondary batteries that utilize various charge and discharge principles in order to obtain battery capacity. In particular, attention has been paid to a secondary battery that utilizes insertion and extraction of an electrode reactant or that utilizes precipitation and dissolution of the electrode reactant, because higher energy density is achieved thereby, compared to energy density in a battery such as a lead battery or a nickel-cadmium battery.
A secondary battery includes a cathode, an anode, and electrolytic solution. The cathode includes a cathode active material related to charge and discharge reactions, and the anode includes an anode active material related to charge and discharge reactions. The electrolytic solution includes a solvent and an electrolyte salt. A configuration of the secondary battery largely influences battery characteristics. Various considerations have been therefore made on the configuration of the secondary battery.
Specifically, in order to improve charge and discharge cycle characteristics, etc., a coating film made of a metal oxide such as beryllium oxide (BeO) is provided on a surface of the cathode (for example, see Japanese Patent No. 3172388). In order to improve thermal stability, etc., the surface of the cathode active material is coated with a metal oxide such as an oxide of magnesium (Mg) (for example, see Japanese Patent No. 3691279). In order to improve charge and discharge efficiency, etc., cyclic ester carbonate such as vinylene carbonate or 4-methylene-1,3-dioxolane-2-one is contained in the solvent (for example, see Japanese Unexamined Patent Application Publication Nos. 2000-058122 and 2007-188861 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-533359). In order to prevent decrease in cycle life, a surface of a carbon material used in the anode is covered with a solid polymer electrolyte (for example, see Japanese Unexamined Patent Application Publication No. H07-235328).